先行音の Time-Intensity Trading Ratio におよぼす効果

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Interuaral intensity or time difference carries the information on the direction of a sound source. But if there is a preceding sound leading the signal (the following sound) this information is masked by the preceding sound and the detection threshold of the following one with interaural intensity difference varies from one with interaural time difference. This fact shows that the effect of the preceding sound on the following one depends on whether the information of direction is carried by interaural intensity difference or interaural time difference. This article describes the effects of the preceding sound on localization of the following one and obtains the time-intensity trading ratio as a function of the intensity of the preceding sound. The results obtained are as follows. 1) The minimum detectable changes of the interaural time difference for the higher frequency tone burst are more influenced by the preceding sound than for the lower frequency tone, and the minimum detectable changes of the interaural intensity difference for the lower frequency tone are a bit more influenced by the preceding sound than for the higher frequency tone (see Fig. 2). 2) The minimum detectable changes of interaural intensity difference for the longer duration are smaller than those for the shorter one. On the other hand, the minimum detectable changes of the interaural time difference for the longer duration are greater than those for the shorter duration (see Fig. 3). 3) The minimum detectable changes of interaural intensity difference are little influenced by the time interval between the preceding sound and the following one, while the minimum detectable changes of interaural time difference are much influenced, and, further, it increases along with an increase of the intensity of the preceding sound (see Fig. 4). 4) The time-intensity trading ratio is more influenced by the preceding sound for the time interval of 5 msec between the preceding sound and following than 25 msec, that is, the trading ratio abruptly increases, in the former situation, along with an increase of the intensity of the preceding sound (see Fig. 6). 5) When the time interval between the preceding sound and the following is 5 msec and the intensity level of the preceding sound is 0 dB relative to that of the following, the trading ratio changes into negative (see Fig. 6). 6) An increase of the trading ratio accompanied by an increase of the intensity of the preceding sound is greater for 5 msec duration than for 20 msec (Fig. 6) These results show that the information of interaural time difference is more easily masked by the preceding sound than one of interaural intensity difference, so that the lateralization is more affected by interaural intensity difference than by interaural time difference when the preceding sound is present. The results may be interpreted as follows. 1) Since the sound with interaural time difference has interaural difference at their onset, while the sound with interaural intensity difference has its difference at the steady part, the information of interaural time difference is more easily masked than one of interaural intensity difference. 2) If the time-intensity trading is caused by neural latency, the slope of the curve of the latency vs. sensation level (see Fig. 10) is regarded as the trading ratio. When the preceding sound is present, the threshold of the following one is raised by the forward masking, and the effective level of the sound decreases. Thus the trading ratio increases according to the curve. The results calculated from the latency curve are shown in Fig. 11, which are consistent with the results of the experiment 2 (Fig 6).
社団法人日本音響学会の論文
1972-01-10

先行音の Time-Intensity Trading Ratio におよぼす効果

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